Age composition and reproductive period o the shad, Konosirus punctatus, in Cheonsu Bay were determined though analysis of sizi, ane and maturity of fish. Sampses were collected with trap in the bay mouth from May, 1981 to December, 1982. Shads start entering the bay for feeding and spawning in spring when water temperature exceeds 8$^{circ}C$. They stay in inner part of the bay in summer nad move out to sea in autumn before water trmperature decreasea to 8$^{circ}C$. Fish grows very rapidly during first summer after birth. Mean lengthes of 1-4 year old fishes were 12.2cm, 15.8cm, 17.6cm and 20.9cm, respectively. The largest and oldrst fish pbserved was 22.0cm long with age 4. Shads of Cheonsu Bay reach maturity at 2 years old at the size greater then 14cm. Data on size and age at first maturityindicate thzt maturity of shad depends on size and not on age. Spawning occurs from late April to late May when water temperature is between 8$^{circ}C$ and 15$^{circ}C$.